Display omitted •Microwave radiation was successfully applied for crude oil demulsification.•Multimode microwave radiation provided faster heating.•Single mode microwave radiation spent less energy.•Total applied energy rules the demulsification efficiency. During petroleum production and refining, water-in-crude oil emulsions are formed in a desirable or undesirable fashion. However, for economic and operational reasons it is necessary to separate water from oil. In order to present an alternative to the currently available techniques used to solve such task, this study aims to analyze the influence of microwave application modes (multimode and single mode) on the breaking efficiency of a synthetic water-in-crude oil emulsion. In both heating modes, it was observed that the water content, temperature, and total applied energy are preponderant parameters regarding obtain higher efficiencies. The single mode heating required less energy to reach the same temperature and/or demulsification efficiency while the multimode provided better reproducibility. The power dissipation and, consequently, the microwave heating efficiency was dependent on the heating temperature and the emulsion water content. Furthermore, it was noticed that the presence of chemical additives tends to minimize any effect of irradiation mode on demulsification efficiency at temperatures above the 120°C.